Cast metallic denture



Patented Sept. 5, 1939 PATENT OFFICE 2,171,144 oAs'r METALLIC DENTURE Cornell Joel Grossman, Millburn, N. J. V I

No Drawing. Application May 23, 1939,

Serial No. 275,230

4 3 Claims. (01. 75-171) This invention relates to metallurgy and more particularly to an alloy suitable for useinthe manufacture of cast dentures and the like.

In the manufacture of metallimdentures the alloy composition employed must be stainless and non-corrosive towards various acid and alkaline re-agents present in the mouth of various foods and liquids. The alloy also must be wear-resistant and the alloy must be variable as to percentages of the several constituents to'a sufiicient' extent and flexibility permitting its use under a wide variety of serviceconditions. Moreover the alloy composition must be adapted to be readily cast free from blow-holes and with a minimum of material surplus, by the ordinary methods I practised in the art.

The present invention aims to provide an alloy adapted to meet these 'many conditions and further aimsto provide a denture comprised of the said alloy. The alloy composition of the present invention comprises a base consisting of cobalt and chromium in such relative proportions of the cobalt to give the required strength, toughness and where resistant propertiesare desired, and

chromium in sufficient amount to render the base stainless and corrosion-resistant. Into this base I may incorporate manganese or silicon or both in such amounts as be necessary to completely deoxidize the alloy and to competely neutralizethe deleterious effect of any sulphur or carbon present in the base and I may also incorporate a percentage of molybdenum or tungsten or both in such an amount as will augment the normal strength and rigidity of'the base. Into thebase or base improved by additions of one or more of the metals manganese, molybdenum and tungsten, I incorporate a sufilcient percentage of boron as will effectively protect the alloy constituents from oxidation during thesubsequent re-melting and casting to form dentures. In the manufacture of dentures it is customary inthe art to melt the alloy in an open crucible by'impinging thereon the open flame of, oxyacetylene, or oxy-hydrogen blow torch. When fully molten the alloy is centrifugally cast into a mold wherein relatively rapid solidification occurs. Heretofore in the art it has been difficult -to manufacture cast dentures of metals in thismanner due to the fact that it is impractical to employa protective slag over the metal during the melting and casting operations, as the-slag, when used, also entered the mold and was entrapped by the rapidity of solidifying metal, causing blow-holes, voids and the like. When however a protective slag was not used during the melting operation of chromium containing alloys excessive oxidation of the metal constituents occurred. and voids caused by oxide and. gas occlusions are obtained. This circumstance has greatly limited the use and' adaptation of chromium-containing alloys, particularly in the forming of cast dentures, due to the fact that when molten or during melting the chromium contents of such an alloy or alloys rapidly oxidize to form diflicultly fusible oxide compounds even though the alloy has been covered or protected by readily fusible slag materials.

I have found that the most effective way to prevent the oxidation of the chromium in chromium containing alloys is to incorporate in the alloy an alloy-constituent which is more readily -oxidisable thanthe chromium and which on oxidation forms a relatively low melting slag operating to protect the alloy from direct contact with oxidizing agents. Boron is the only alloy constituent of which I am aware that will accomplish this desired result,

The amount of boron I may incorporate in the alloy composition of the present invention may vary widely without departure. I have successfully employed as low as 1.00% and as high as 10%. UnderWery expert manipulating conditions' of melting and casting a boron content of less than 1.0% probably can be employed but under the ordinary manipulating conditions of melting and casting I prefer to have present in my alloy about 5.0% boron, as this amount permits of repeated re-melting without detrimental results to the alloy. The excess boron does not appear to be deleterious in the alloy but to the contrary appears to increase the fluidity of the alloy when molten and the ease with which it may be cast, and cast dentures of my alloy containing 5.0% or more of boron appear to be more 'sharply defined than those containing 1 to 2% boron. This amount of boron, moreover, appears to beneficially affect the physical properties of the alloy, making it of finer grain structure and improving its hardness and luster.

. In my alloy composition I prefer to limit any iron content to less than 1.00%. Iron in amounts greater than this, while being of advantage in some respects, such as giving added strength and ductility, detrimentally affect the corrosion resistance properties and require added chromium to counteract the same. For this reason I prefer to limit my invention to a cobalt chromium base withiron less than 1.0%. In this base alloy .the chromium content may vary from 5% to 45% and the cobalt content may vary from 45% to 94% with the remainder of the alloy consisting of 7 part of the cobalt and in this respect the cobalt,

of the present invention I sometimes prefer a molybdenum and tungsten are to be considered to be substantial equivalents, although each in addition contribute to the corrosion resistant properties of the alloy. The molybdenum conte'nt may be as high as 8% but preferably should be in the range 2 to 4%, The tungsten content may be as high as 4%, but preferably should be in range of 1 to 2%.

As an example of the present invention, alloys that I have found most suitable for general purpose used in the casting of dentures have the following analyses:

I II III Percent Percent Percent Chromium 12M 25 7% 12% 6 7% 62 80 6 5 1 l 0 0 1 max. 0 0 1 0 Alloys suitable for the same purpose but stronger and more suitable for bridge-work are similar to composition No. l, but contain molybdenum 2-8% with the cobalt reduced a corresponding amount or tungsten l-4% with the cobalt reduced to a corresponding amount.

Where'a softer alloy is desired, as in forming of pins, bars and the like, which subsequently are to be bent in shape, I increase the cobalt content to about 90% and lower the chromium contents to less than with about 1% of boron or manganese or 1% of both manganese and boron. The boron content of this alloy operates to facilitatethe subsequent weld attachment of these pins, or bars, or clasps to a cast denture and even permits the casting of the denture directly unto the pin or clasp as heretofore practised in the art with other metals.

In the manufacture of the alloy composition chromium titanium alloy instead of chromium as an ingredient and a manganese boron alloy. These alloys should be preferably substantially free from carbonand from. iron. I then mix the chromium, titanium and manganese boron alloys together with cobalt, preferably in small-sized pieces, in such relative amounts as will give me the alloy composition desired, and melt the some down in the electric induction furnace under conditions protecting the metal from oxidation. When fully molten the alloy is cast in the mold adapted to form relatively small diameter rods which after solidification may be cut or broken into relatively small pieces.

In the forming of dentures of this alloy, a sui'ficient amount of these small-sized pieces of rod is placed in an open crucible and is melted by the direct application thereon of the oxyacetylene or oily-hydrogen flame and as soon as the metal becomes molten and fluid the molten metal is cast centrifugally into the denture mold as heretofore practised in the art. The thus formed cast denture will be substantially free from blow-' holes, voids or oxide and slag inclusions. Any boron which is oxidized during the melting prior to casting, forms such a fluid slag that on entering the mold during casting the same does not interfere with the entrance of the molten metal into the finest crevices of the mold, and a clearly defined sound casting will be obtained.

Satisfactory dentures may be cast from an alloy of 3% to 10% of chromium; 3% to 10% titanium; 1 to 10% boron, balance cobalt.

For greater rigidity the chromium is increased and excellent dentures are obtainable from a casting alloy comprising 345% chromium; l-l0% boron; .2-2% silicon; .2-5% manganese; .2-% titanium; balance cobalt. The titanium and chromium can be added as a titanium chromium alloy. The boron content may be increased without deleterious efiect.

From the above description of the present invention, it will be apparent that the same'may be widely varied as to alloy composition without departure from the invention and all such modifications and variations are contemplated as may fall within the scope of the following claims.

What I claim is:

3. A casting alloy for denture and the like,

comprising .5-l5% boron; l-% titanium; 345% chromium; balance cobalt.

CORNEIL JOEL GROSSMAN.

- .45 1. An alloy suitable for use in the manufacture boron; v 

